svcrdma: Implement multi-stage Read completion again

Having an nfsd thread waiting for an RDMA Read completion is
problematic if the Read responder (ie, the client) stops responding.
We need to go back to handling RDMA Reads by getting the svc scheduler
to call svc_rdma_recvfrom() a second time to finish building an RPC
message after a Read completion.

This is the final patch, and makes several changes that have to
happen concurrently:

1. svc_rdma_process_read_list no longer waits for a completion, but
   simply builds and posts the Read WRs.

2. svc_rdma_read_done() now queues a completed Read on
   sc_read_complete_q for later processing rather than calling
   complete().

3. The completed RPC message is no longer built in the
   svc_rdma_process_read_list() path. Finishing the message is now
   done in svc_rdma_recvfrom() when it notices work on the
   sc_read_complete_q. The "finish building this RPC message" code
   is removed from the svc_rdma_process_read_list() path.

This arrangement avoids the need for an nfsd thread to wait for an
RDMA Read non-interruptibly without a timeout. It's basically the
same code structure that Tom Tucker used for Read chunks along with
some clean-up and modernization.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
index c98d29e51b9c..e7595ae62fe2 100644
--- a/include/linux/sunrpc/svc_rdma.h
+++ b/include/linux/sunrpc/svc_rdma.h
@@ -170,8 +170,6 @@ struct svc_rdma_chunk_ctxt {
 	struct list_head	cc_rwctxts;
 	ktime_t			cc_posttime;
 	int			cc_sqecount;
-	enum ib_wc_status	cc_status;
-	struct completion	cc_done;
 };
 
 struct svc_rdma_recv_ctxt {
@@ -191,6 +189,7 @@ struct svc_rdma_recv_ctxt {
 	unsigned int		rc_pageoff;
 	unsigned int		rc_curpage;
 	unsigned int		rc_readbytes;
+	struct xdr_buf		rc_saved_arg;
 	struct svc_rdma_chunk_ctxt	rc_cc;
 
 	struct svc_rdma_pcl	rc_call_pcl;
@@ -240,6 +239,9 @@ extern int svc_rdma_recvfrom(struct svc_rqst *);
 extern void svc_rdma_destroy_rw_ctxts(struct svcxprt_rdma *rdma);
 extern void svc_rdma_cc_init(struct svcxprt_rdma *rdma,
 			     struct svc_rdma_chunk_ctxt *cc);
+extern void svc_rdma_cc_release(struct svcxprt_rdma *rdma,
+				struct svc_rdma_chunk_ctxt *cc,
+				enum dma_data_direction dir);
 extern int svc_rdma_send_write_chunk(struct svcxprt_rdma *rdma,
 				     const struct svc_rdma_chunk *chunk,
 				     const struct xdr_buf *xdr);